A solenoid valve of a type that opens and closes a valve member in a direct-acting manner by using a movable iron core of a solenoid operation portion is known, as is disclosed, for example, in Japanese Unexamined Patent Application Publication No. 2004-156709.
A solenoid valve of this type generally comprises a fixed iron core and a movable iron core that adhere to each other by a magnetic force generated by energizing an exciting coil, a poppet-type valve member that attaches to and detaches from a valve seat by an action of the movable iron core to close and open a flow path, an iron core return spring that biases the movable iron core toward an initial position (a valve-closing position at which the valve member abuts on the valve seat) at which the movable iron core is detached from the fixed iron core, and a valve return spring that biases the valve member in a direction in which the valve member detaches from the valve seat.
The solenoid valve is constructed such that, when the exciting coil is not energized, the movable iron core is detached from the fixed iron core by a biasing force of the iron core return spring, and the valve member is pressed against the valve seat via the movable iron core to close the flow path. The solenoid valve is also constructed such that, if the exciting coil is energized, since the movable iron core adheres to the fixed iron core and the biasing force of the iron core return spring no longer acts on the valve member, the valve member is detached from the valve seat by a biasing force of the valve return spring to open the flow path.
However, if the solenoid valve is switched from a valve-opening state in which the exciting coil is energized and the iron core return spring is compressed by the movable iron core to the valve-closing state by turning off the energization to the exciting coil, the movable iron core detaches from the fixed iron core at high velocity, causing the valve member to hit the valve seat with high impact by a inertial force of the movable iron core. Thus, there is a problem that the valve member is easily worn away. Also, there is another problem that a transmission member (a pushrod) provided between the movable iron core and the valve member to transmit an acting force of the movable iron core to the valve member is easily worn away.